linux-kernel - Re: [PATCH 01/10] irqchip: irq-mips-gic: export gic_send

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Date:	Fri, 28 Aug 2015 16:22:08 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Qais Yousef <qais.yousef@...tec.com>
cc:	Marc Zyngier <marc.zyngier@....com>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	Jason Cooper <jason@...edaemon.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Mark Brown <broonie@...nel.org>,
	Lisa Parratt <Lisa.Parratt@...tec.com>
Subject: Re: [PATCH 01/10] irqchip: irq-mips-gic: export gic_send_ipi

On Fri, 28 Aug 2015, Qais Yousef wrote:
> Thanks a lot for the detailed explanation. I wasn't looking for a quick and
> dirty solution but my view of the problem is much simpler than yours so my
> idea of a solution would look quick and dirty. I have a better appreciation of
> the problem now and a way to approach it :-)
> 
> From DT point of view are we OK with this form then
> 
>     coprocessor {
>             interrupt-source = <&intc INT_SPEC COP_HWAFFINITY>;
>             interrupt-sink = <&intc INT_SPEC CPU_HWAFFINITY>;
>     }
> 
> and if the root controller sends normal IPI as it sends normal device
> interrupts then interrupt-sink can be a standard interrupts property (like in
> my case)
> 
>     coprocessor {
>             interrupt-source = <&intc INT_SPEC COP_HWAFFINITY>;
>             interrupts = <INT_SPEC>;
>     }
> 
> Does this look right to you? Is there something else that needs to be covered
> still?

I'm not an DT wizard. I leave that to the DT experts.
 
> One more thing I can think of now is that the coprocessor will need the raw
> irq numbers that are picked by linux so that it can use them to trigger the
> IPI. Are we ok to add a function that returns this raw irq number (as opposed
> to linux irq number) directly from DT? The way this is communicated to the
> coprocessor will be platform specific.

Why do you want that to be hacked into DT? 

> >     To configure your coprocessor proper, we need a translation
> >     mechanism from the linux interrupt number to the magic value which
> >     needs to be written into the trigger register when the coprocessor
> >     wants to send an interrupt or an IPI.
> > 
> >     int irq_get_irq_hwcfg(unsigned int irq, struct irq_hwcfg *cfg);
> > 
> >     struct irq_hwcfg needs to be defined, but it might look like this:
> > 
> >       {
> > 	/* Generic fields */
> > 	x;
> > 	...
> > 	union {
> > 	      mips_gic;
> > 	      ...
> > 	};
> >       };

That function provides you the information which you have to hand over
to your coprocessor firmware.

Thanks,

	tglx
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